In the past, cooling fans have been used in a wide variety of environments, including with avionics equipment on an aircraft. In some aircraft, it is desirable to have cooling fans which are controllable over a wide range of conditions. In some avionics boxes, in the past, these fans were often turned by brushless DC motors, which were controlled by specialized controllers, such as trapezoidal drivers. It has also been well known to use AC motors for many purposes. Often, these motor controllers are speed controlled with a Pulse Width Modulated (PWM) motor drive voltage.
While these cooling systems may have many advantages in particular uses, they also have created challenges. One common challenge created by these designs is the relatively high cost. Additionally, these PWM controllers are relatively complex and require circuitry which is too large for the form factors of some avionics applications. Furthermore, PWM controllers of the drive voltage of AC motors often produce a relatively high level of electromagnetic interference (EMI), which may then require costly, bulky and heavy shielding in some applications.
Consequently, there exists a need for improved methods and apparatuses for cooling avionics equipment.